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ABRASIVE/ GRINDING/ GRINDING MACHINES |
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Precision Grinding System Triples Process Capability |
| A turnkey
grinding system with automatic loaders makes several versions of a front
wheel drive hub with a surface finish of 0.8 Ra and a 5.6 Cpk, producing
about 105 parts per hour.
In the world of precision grinding, improvements in process capability (Cpk) are often measured in fractions of a point. An acceptable industry target for a process that is under control is usually defined by a Cpk of 1.33. However, engineers and managers at G. W. King Ltd., in Letchworth, England, require a Cpk of 1.67 for their grinding operation. When the Midas grinders from Weldon Machine Tool Inc. (York, PA) were able to demonstrate a Cpk of 5.6, King's project manager, Dave Hunt, and others were impressed. "It's not very often that a product or process exceeds our standards by that magnitude," he says. "Our Weldon grinders have given us an important advantage in the marketplace." King is a subcontractor to the automotive industry, providing wheel hub components and assemblies to major automakers such as Land Rover, BMW, and Ford. The company began working with Weldon in 1995 after receiving a contract with Land Rover to produce wheel hubs for their Range Rover, Discovery, and Freelander sport utility vehicles (SUVs). To maintain peak efficiency for the contract, King determined that they needed a fast, effective way to grind both sides of the wheel hubs. Company engineers knew that they would need an automated system, but they also were looking for help with process development. Weldon responded with a turnkey package built around its model 120A Midas production grinders with automatic loaders. The resulting system grinds the hubs in two separate operations, each on a different machine. In the first operation, one side of each hub is finish ground to the bearing diameter, adjacent radius, and bearing shoulder in a single plunge. In the second operation, the other side of the hub is finish ground to the locating diameter, flange face, and adjacent radius, also in a single plunge. The hubs are made of hardened 58HRC steel. They vary in size from 2" to 4" in overall length, from 5" to 6" in diameter, with a grind diameter of up to 2", and flange faces as high as 1_". The Weldon grinders remove 0.010" of stock from the diameter of the hubs, and about 0.005" from the face. The flange face must be concave by 10 to 16 microns, with this feature dressed into the wheel. Print tolerances are: diameter size, ñ 0.0065 mm; roundness, 0.010 mm; spline/bearing runout, 0.40 mm; surface finish, 0.8 Ra; and face runout, 0.030 mm to bearing diameter. King installed two Weldon Midas 120A grinders in 1995 and has since added four more. All of the machines feature automatic loaders to load and unload parts from an automated conveyor system carrying hubs through the manufacturing process. With its new setup, King is able to grind Land Rover parts with a floor-to-floor cycle time of 34 seconds, including 18 seconds of actual grind time - around the clock, 24 hours per day. The machines are able to grind 25 parts between wheel dressing cycles. Weldon's Midas series CNC (computer numerical control) cylindrical grinders are designed to be used in virtually any high-production setting, including automotive, heating and refrigeration, fluid power, power hand tool, aircraft, and aerospace industries. Process capabilities include formed wheel plunge, CNC multi-plunge, and high-speed CBN (cubic boron nitride) contour grinding. The grinders can be configured with either a straight or angular wheelhead, which is fixed at the factory. Each Midas model 120A angle wheelhead production grinder at King is equipped with:
"What initially sold us on Weldon's package was their low cycle time and the excellent quality of the finished parts produced by their grinders," Hunt explains. "Since then, we've also been favorably impressed with Weldon's customer service. Weldon has literally become a partner in our success." |